This application claims priority to a PCT Application filed on Dec. 8, 2000 and assigned Application No. PCT/SE00/02467 which was published on Jun. 28, 2001 and assigned International Publication No. WO 01/46933 A1; the PCT Application claims priority to an application filed in Sweden on Dec. 22, 1999 and assigned Application No. 9904717-7, the contents of both applications are incorporated herein by reference.
1. Field of the Invention
The invention relates to a system and a method for avoidance of collision between vehicles.
2. Description of the Related Art
Collisions between fighting airplanes during air combat training is frequently occurring and are normally caused by a pilot lacking of attention, for instance due to attention being directed to radar reconnaissance or weapon adjustments. These collisions cause costly losses in the form of crashed fighting airplanes and, in the worst case, result in the loss of life of an involved pilot. Consequently, there is a great need of a reliable system for collision avoidance.
Conventional collision avoidance systems are based on the idea to calculate the trajectories of the involved airplanes and predict a risk of collision with the aid thereof. Such a collision avoidance system, which primarily has been developed and used for civil air traffic, is known under the denomination TCAS (xe2x80x9cTraffic alert and Collision Avoidance Systemxe2x80x9d). Each airplane included by this system is provided with its own TCAS-device comprising inter alia a radio transponder. The radio transponder continuously transmits a radio signal and a radio transponder in another airplane, when receiving this radio signal, transmits a reply signal comprising data concerning the height of flight of the own airplane. The distance to the other airplane is obtained by measuring the time between transmitted and received signal and the bearing is obtained by means of a radio direction finder. By means of these values the TCAS-device continuously calculates and updates the flight trajectories for the TCAS-equipped airplanes located in the surroundings. If a flight trajectory calculated for another airplane is estimated to cross the planned flight trajectory of the own airplane, a warning is generated to the pilot at a moment with a predetermined time interval up to a so called xe2x80x9cClosest Point of Approachxe2x80x9d.
TCAS II is a further developed system which besides giving the pilot a warning also suggests an avoidance manoeuvre direction. The avoidance manoeuvre directions are co-ordinated between the involved airplanes via radio link. TCAS gives a bad accuracy in the bearing values and many warnings are generated even when the airplanes can pass each other without any risk of collision.
A collision avoidance system that gives many superfluous warnings implies an additional stress factor for the pilot, which is particularly inconvenient in air combat training when the pilot has a very high work load with many instruments and a large amount of data to handle under great pressure. During air combat training with flight manoeuvres that are difficult to predict and a close contact between the involved airplanes, the risk of superfluous warnings is as well larger than in commercial aviation.
An object of the present invention is to provide a system and a method for collision avoidance, particularly for use in fighting airplanes, by means of which collisions between vehicles can be averted with a high reliability at the same time as collision warnings and/or automatic avoidance manoeuvres are avoided to the utmost possible extent in the situations when the vehicles located in the vicinity of each other have a possibility to pass each other without any risk of collision.
The system and the method according to the invention are based on the strategy to seek for a possible avoidance manoeuvre for the respective vehicle and present a warning to a person manoeuvring the vehicle and/or automatically execute the suitable avoidance manoeuvre just before the possibility to perform this avoidance manoeuvre disappears, i.e. just before the involved vehicles are in such a position in relation to each other that a collision cannot be avoided with a satisfactory security. The collision avoidance system according to the invention is consequently restricted and a warning is generated and/or an automatic avoidance manoeuvre is performed only in case of an immediate risk of collision.
According to a preferred embodiment of the invention, a calculated avoidance manoeuvre trajectory is represented by a number of three dimensional objects, such as spheres, each of which objects being assigned a certain time value, the dimension of the separate objects being dependent on the stipulated minimum distance between the avoidance manoeuvre trajectories. In this connection, it is controlled whether any of the geometrical object representing the avoidance manoeuvre trajectory of the vehicle is overlapping a geometrical object with corresponding time value included in the representation of the avoidance manoeuvre trajectories of any of the other vehicles. In this way it becomes possible to control in an easy way whether the calculated avoidance manoeuvre trajectories are located to close to each other.
By making the dimension of the geometrical objects depend also on estimated errors of the calculated avoidance manoeuvre trajectories, an improved security against collisions caused by miscalculations is obtained.
According to a preferred embodiment of the invention, the avoidance manoeuvre direction for the respective vehicle is determined based on the criteria that the completion points of the avoidance manoeuvre trajectories of the vehicles are to be at as large a distance from each other as possible. In this way, the appropriate avoidance manoeuvre directions can be calculated by means of a relatively simple model of calculation.